The kinetics of anation of [Cr(S-pdtra)(H2O)] and [Cr(edtrp)(H2O)] complexes (S-pdtra=S-propane-1,2-diamine-N,N,N -triacetate, edtrp=ethylenediamine-N, N,N-tripropionate) by thiocyanates and aquation of the [Cr(NCS)(S-pdtra)]– and [Cr(NCS)(edtrp)]– ions have been studied in aqueous HClO4 solutions. The rate laws and the activation parameters have been determined and discussed. The observed decrease in reactivity for the edtrp complexes corresponds with a changeover of the reaction mechanism from Ia to Id for reactions of the CrIII-S-pdtra and CrIII-edtrp species, respectively. 相似文献
Several years have passed since the medical and scientific communities leaned toward tissue engineering as the most promising field to aid bone diseases and defects resulting from degenerative conditions or trauma. Owing to their histocompatibility and non-immunogenicity, bone grafts, precisely autografts, have long been the gold standard in bone tissue therapies. However, due to issues associated with grafting, especially the surgical risks and soaring prices of the procedures, alternatives are being extensively sought and researched. Fibrous and non-fibrous materials, synthetic substitutes, or cell-based products are just a few examples of research directions explored as potential solutions. A very promising subgroup of these replacements involves hydrogels. Biomaterials resembling the bone extracellular matrix and therefore acting as 3D scaffolds, providing the appropriate mechanical support and basis for cell growth and tissue regeneration. Additional possibility of using various stimuli in the form of growth factors, cells, etc., within the hydrogel structure, extends their use as bioactive agent delivery platforms and acts in favor of their further directed development. The aim of this review is to bring the reader closer to the fascinating subject of hydrogel scaffolds and present the potential of these materials, applied in bone and cartilage tissue engineering and regeneration. 相似文献
The mechanochemical cycloreversion of 1,2,3-triazole compounds, which serve as unusually stable building blocks in materials and biomolecular chemistry as a result of mild “click chemistry”, remains puzzling. We show that the hitherto discussed straight-forward retro-click mechanism of the 1,4-disubstituted isomer, even if CuI catalyzed, can be ruled out in view of more favorable activation free energies of destructive pathways. In stark contrast, the 1,5-regioiomer can undergo cycloreversion under rather mild mechanochemical conditions owing to its favorable response to the external force in conjunction with standard RuII catalysis. 相似文献
This article presents studies on iron speciation in the pottery obtained from archaeological sites. The determination of iron forms Fe(II) and Fe(III) has been provided by a very simple test that is available for routine analysis involving the technique of molecular absorption spectrophotometry (UV–Vis) in the acid leachable fraction of pottery. The elemental composition of the acid leachable fraction has been determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Additionally, the total concentration of the selected elements has been determined by X-ray fluorescence spectrometry with energy dispersion (EDXRF). The results of the iron forms’ determinations in archaeological pottery samples have been applied in the archaeometric studies on the potential recognition of the pottery production technology, definitely going beyond the traditional analysis of the pottery colour. 相似文献
This work was aimed at studying variations in the termination mechanism occurring during the after‐effects of a light‐induced polymerization of a dimethacrylate monomer after the irradiation had been discontinued. The experimental method was based on differential scanning calorimetry. The initiation was stopped at various moments of the reaction corresponding to different degrees of double‐bond conversion (starting conversions). Three termination models: monomolecular, bimolecular, and mixed were used to calculate the ratio of the bimolecular termination and propagation rate coefficients ktb/kp and/or the monomolecular termination rate coefficient ktm. The models were determined over short time intervals (conversion increments) of the dark reaction giving different values of rate coefficients for each time interval (interval approximation method). Two‐stage statistical analysis was used to find the model that best reproduced the experimental data obtained for each conversion increment. This enabled variations in the termination mechanism during the after‐effects to be followed. It was found that the termination mechanism changed with the time of the dark reaction from the bimolecular reaction to the mixed reaction when the light was cut off at low and medium double‐bond conversions. At higher starting conversions a monomolecular termination mechanism dominated from the beginning of the dark reaction. The mixed termination model was the only model to describe correctly the variations of rate coefficients in the dark, i. e., the increase in ktm and the decreasein the ktb/kp ratio. 相似文献
The primary reason behind the search for novel organic materials for application in thermoelectric devices is the toxicity of inorganic substances and the difficulties associated with their processing for the production of thin, flexible layers. When Thomas Seebeck described a new phenomenon in Berlin in 1820, nobody could have predicted the future applications of the thermoelectric effect. Now, thermoelectric generators (TEGs) are used in watches, and thermoelectric coolers (TECs) are applied in cars, computers, and various laboratory equipment. Nevertheless, the future of thermoelectric materials lies in organic compounds. This paper discusses the developments made in thermoelectric materials, including small molecules, polymers, molecular junctions, and their applications as TEGs and/or TECs. 相似文献
New mechanism of cationic polymerization of cyclic ethers and acetals consisting in the activated (e.g. protonated) monomer addition to the electrically neutral macromolecule e.g.: is discussed. It is shown, that when the -OH in the tail-group is more nucleophilic than monomer itself this mechanism has chances to dominate over the traditional mechanism of propagation, involving tertiary oxonium ion. Kinetics of the polymerization process, elementary reactions, competition with the tertiary oxonium ion growth are discussed. Examples are given, based on the work on ethylene oxide and epichlorohydrin polymerization, showing how to apply the theory of the activated monomer in order to avoid side reactions, namely cyclization and disproportionation of the chains. 相似文献
Single crystals of [Eu(C4H4O6)(H2O)2](H2O)2 were obtained from the combination of solutions of EuCl2, previously obtained by electrolysis of an aqueous solution of EuCl3, and tartraric acid, neutralized by LiOH. The crystal structure (orthorhombic, P212121, Z = 4, a = 948.9(1), b = 954.6(1), c = 1098.4(1) pm; R(F) = 0.0242 and Rw(F2) = 0.0585 for I > 2σ(I); R(F) = 0.0256 and Rw(F2) = 0.0592 for all data) is isotypic with [Ca(C4H4O6)(H2O)2](H2O)2 and [Sr(C4H4O6)(H2O)2](H2O)2 exhibiting a three‐dimensional structure. The divalent cations (Eu2+, Ca2+, Sr2+) are eight‐coordinate by oxygen atoms that originate from carboxylate and hydroxyl groups of the tartraric dianion and two of the four water molecules. 相似文献
A novel and unexpected convenient one-pot synthesis of 1,2,3,4-thiatriazoles has been discovered while investigating the classical tetrazine “Pinner synthesis”. The synthetic route starts from commercially-available nitrile derivatives and gives good to high yields (51–80 %) with no need to isolate any thioacylating agents. The crucial impact of the solvent on the outcome of the modified “Pinner synthesis” is moreover examined and discussed. Using this new synthetic route, a novel donor-acceptor thiatriazole derivative has been prepared, which exhibits prominent thermally-activated delayed fluorescence (TADF) in both solution and film. The photoluminescence quantum yield (PLQY) in methylcyclohexane (MCH) and Zeonex (a cyclo olefin polymer) in oxygen-free conditions were determined to be 76 and 99 %, respectively. This work provides an efficient and practical synthetic approach to functionalized 1,2,3,4-thiatriazole derivatives, and will noticeably facilitate the application of 1,2,3,4-thiatriazole as an electron acceptor in organic electronics. 相似文献
Evidence for the activated monomer (AM) mechanism operating in the polymerization of propylene oxide (PO) initiated with HBF4 is presented. The contribution of AM route of propagation is the highest and formation of cyclic oligomers mostly suppressed when monomer concentration is low enough. This was achieved by slowly adding PO to the reaction mixture, as previously proposed on the basis of kinetic considerations. 相似文献